A Head-Up Display (HUD) is any transparent display that presents data without requiring users to look away from their usual viewpoints. Although they were initially developed for military aviation, HUDs are now used in commercial aircraft, automobiles, and other applications. Typically, a HUD system mainly includes a combiner, a projector, and a video data source such as a computer. The combiner is a semi-transparent mirror that is positioned in front of the driver/pilot to display the virtual picture with the required information projected from the projector. In operation, the combiner can be moved between a parking position when not needed and an operating position when needed. The movement of the combiner between the parking position and the operating position is realized by means of a HUD positioning system. A second function for angular fine adjustment of the combiner is also implemented in such a positioning system for correcting the tilt angle of the combiner depending on driver's height and his eye position.
For example, US2009/0086329A1 disclosed a positioning system for a combiner in a head-up display. In this art, the combiner is moved from a protected parking position to an operating position by a screw spindle coupled to a stepping motor. The movement is guided by side walls with cams and teeth to drive a synchronous movement. It includes the possibility for angular adjustment of combiner position when reaching the operating position. However, the required space for such a positioning system including many parts for accurate movement limits the possibilities for reducing the size of the HUD system. Besides, the design does not offer the wished flexibility to follow requirements for dashboard and different windshields from car makers. Additionally, the two major functions, i.e. the combiner movement and the combiner adjustment, are strongly linked with each other so that the design of the mechanism of the combiner movement and combiner adjustment is unchangeable.